1. Field of the Invention
The present invention relates to a lens barrel, and also relates to a zoom lens barrel.
2. Description of the Related Art
As an example of a conventional lens barrel in which two or more lens groups move in an optical axis direction, a lens barrel in which front and rear lens groups are guided linearly in the optical axis direction without rotating about the optical axis and in which the lens support frame of each of the front and rear lens groups is provided with a set of follower pins which are respectively engaged in a corresponding set of cam grooves (cam slots) formed on a cam ring is known in the art. In this type of lens barrel, one cam groove is necessary for each follower pin formed on the lens support frame of each of the front and rear lens groups.
Accordingly, a large number of cam grooves are necessary if the lens barrel is provided with a plurality of movable lens groups. It is difficult to form a large number of cam grooves on a cam ring due to a limited circumferential area thereon. This is more serious if the diameter of the cam ring is small.
One possible solution would be to increase the pitch of each cam groove (i.e., to increase the angle of inclination of each cam groove relative to a circumferential direction of the cam ring), however, this impairs the movement of the follower pins, or may lock the follower pins. If the number of the follower pins is large, the number of the cam grooves formed on the cam ring is also large, which inevitably deteriorates the strength of the cam ring.
As an example of a conventional extendable lens barrel such as an extendable zoom lens barrel in which two or more lens groups move in an optical axis direction, an extendable lens barrel in which front and rear lens groups are guided linearly in the optical axis direction without rotating about the optical axis, and in which the lens support frame of each of the front and rear lens groups is provided with a set of follower pins which are respectively engaged in a corresponding set of cam grooves (cam slots) formed on a cam ring, is known in the art. Note that the term xe2x80x98extendable lens barrelxe2x80x99 refers to a lens barrel which extends and retracts so that the length thereof is shortest at an accommodation position, and is longer at a photographing position.
In such an extendable lens barrel, if the lens barrel is retracted to move each of the front and rear lens groups to an accommodation position thereof, each follower pin of the lens support frame of each lens group is accommodated and positioned at an end (accommodation position) of the associated cam groove with no gap between the follower pin and the end of the cam groove, and accordingly, each follower pin cannot move from the accommodation position thereof unless the extendable lens barrel is extended to move each of the front and rear lens groups out of the accommodation position thereof.
However, if the respective accommodation positions of the front and rear lens groups are precisely determined by the profiles of the cam grooves, the front and rear lens groups at their respective accommodation positions need to have a certain gap therebetween so as not to collide with each other, which makes it difficult to reduce the length of the extendable lens barrel in an accommodation state thereof.
In addition, since it is necessary to adjust the fixing position of at least one lens group relative to a support frame thereof in the optical axis direction when the lens group is fixed to the lens support frame during assembly, a marginal space for the fixing position adjustment needs to be secured between the respective accommodation positions of adjacent lens groups, which makes it more difficult to reduce the length of the extendable lens barrel in an accommodation state thereof.
In an extendable lens barrel which extends and retracts between an extended position (ready-to-photograph position) and an accommodation position, if it is desired to reduce the length of the extendable lens barrel in an accommodation state thereof, all of the movable lens groups positioned in the lens barrel need to be retracted in order to be as compact as possible in an accommodation position of the extendable lens barrel.
However, in the case where the extendable lens barrel is provided at the front end thereof with a photographing aperture and at least one lens barrier blade which opens and closes the photographing aperture in a plane perpendicular to the optical axis of the extendable lens barrel, a substantial gap has to be provided between the front surface of the front-end lens group and the lens barrier blade, which increases the length of the extendable lens barrel.
The present invention provides a lens barrel wherein a cam ring does not need to have a large diameter even if the lens barrel is provided with a large number of movable lens groups, and wherein the cam ring can be provided with cam grooves which ensure smooth movements of the associated follower pins while keeping any decrease in strength of the cam ring to a minimum.
The present invention also provides a lens barrel wherein each of a plurality of lens groups provided in the lens barrel can be accommodated (housed) as compact as possible while preventing adjacent lens groups from contacting with each other even if the lens barrel is of a type wherein at least one lens group is fixed to the lens support frame thereof while the fixing position of the lens group is being adjusted relative to the lens support frame thereof in the optical axis direction, or even if the lens barrel is an extendable lens barrel provided at the front end thereof with a photographing aperture and at least one lens barrier blade which opens and closes the photographing aperture.
The present invention also provides a extendable zoom lens barrel having two or more movable lens groups, wherein front and rear lens groups can be accommodated compact in size in the zoom lens barrel when it is in an accommodation state.
For example, in an embodiment, a lens barrel is provided, including first and second lens groups guided in an optical axis direction without rotating about the optical axis; a first support frame which supports the first lens group, the first support frame including a first cam follower; a second support frame which supports the second lens group, the second support frame including a second cam follower; and a cam ring which is driven to rotate about the optical axis, the cam ring including a cam groove in which the first cam follower and the second cam follower are engaged. The cam groove is formed as a continuous groove and includes a first groove portion via which the first cam follower is guided to move the first lens group, and a second groove portion via which the second cam follower is guided to move the second lens group. The cam groove is formed so that one of the first cam follower and the second cam follower enters a corresponding one of the first groove portion and the second groove portion after passing through the other of the first groove portion and the second groove portion in a preparation stage of the lens barrel.
The first groove portion can include a first zooming section for moving the first lens group to perform a zooming operation; and a first accommodation section in which the first cam follower is positioned when the first lens group is accommodated. The second groove portion can include a second zooming section for moving the second lens group to perform the zooming operation; and a second accommodation section in which the second cam follower is positioned when the first lens group is accommodated. The first zooming section, the second zooming section, the first accommodation section and the second accommodation section are arranged in that order from one end of the cam groove, so that the first cam follower passes through the second zooming section when moving between the first accommodation section and the first zooming section.
It is desirable for the first lens group to be positioned in front of the second lens group.
Each of the first lens group and the second lens group can constitute a lens element of a zoom lens optical system, the cam ring being driven to move the first lens group and the second lens group in the optical axis direction while changing a distance therebetween to vary a focal length.
The lens barrel can further include a third lens group positioned behind the second lens group and guided in the optical axis direction, wherein the third lens group constitutes a focusing lens and is moved in the optical axis direction to perform a focusing operation.
In another embodiment, a lens barrel includes a front lens support member which supports a front lens group and is guided in an optical axis direction without rotating about the optical axis; a rear lens support member which supports a rear lens group and is guided in the optical axis direction without rotating about the optical axis; and a support frame movement mechanism for moving the front lens support member and the rear lens support member between respective ready-to-photograph positions and respective accommodation positions located behind the respective ready-to-photograph positions, in the optical axis direction. The support frame movement mechanism brings the front lens support member and the rear lens support member into contact with each other at the respective accommodation positions without causing the front lens group and the second lens group to come into contact with each other.
The support frame movement mechanism can include a biasing device; the support frame movement mechanism can bring the front lens support member and the rear lens support member into contact with each other, with a biasing force of the biasing device, at the respective accommodation positions.
The support frame movement mechanism can include a first cam follower formed on the front lens support member; a second cam follower formed on the rear lens support member; and a cam ring which is driven to rotate about the optical axis, the cam ring including a cam groove in which the first cam follower and the second cam follower are engaged. The cam groove can include a front lens group moving section for moving the front lens support member to the ready-to-photograph position; a rear lens group moving section for moving the rear lens support member to the ready-to-photograph position; a front lens group accommodation section for allowing the front lens group to move to the accommodation position which is located behind a position of the front lens group in the optical axis direction when the first cam follower is positioned in the front lens group moving section; and a rear lens group accommodation section for allowing the rear lens group to move to the accommodation position which is located behind a position of the rear lens group in the optical axis direction when the second cam follower is positioned in the rear lens group moving section. The front lens group accommodation section defines a clearance between the front lens group accommodation section and the first cam follower so that the first cam follower is movable in the optical axis direction in the front lens group accommodation section. The rear lens group accommodation section defines a clearance between the rear lens group accommodation section and the second cam follower so that the second cam follower is movable in the optical axis direction in the rear lens group accommodation section.
The front lens group moving section and the rear lens group moving section constitute a first zooming section and a second zooming section, respectively, for varying a focal length to perform a zooming operation.
The biasing device can bias the front lens support member in a direction toward the accommodation position so that the front lens support member moves to come in contact with the rear lens support member.
It is desirable for an area of the front lens group accommodation section to be smaller than an area of the rear lens group accommodation section.
In another embodiment, lens barrel having an optical system including of a plurality of lens groups, the lens barrel including a lens supporting frame to which a frontmost lens group of the plurality of lens groups is supported; a first moving frame to which the lens supporting frame is supported via male and female screw-threaded portions meshing with each other, one and the other of the male and female screw-threaded portions being formed on the lens supporting frame and the first moving frame, respectively; a second moving frame to which a rear lens group of the plurality of lens groups which is positioned behind the frontmost lens group is supported; and a support frame movement mechanism for moving the first moving frame and the second moving frame between respective ready-to-photograph positions and respective accommodation positions located behind the respective ready-to-photograph positions in a direction of an optical axis. A supporting position of the lens supporting frame, relative to the first moving frame in the optical axis direction, can be adjusted via the male and female screw-threaded portions during assembly. The support frame movement mechanism brings the lens supporting frame and the second moving frame into contact with each other when positioning the first moving frame and the second moving frame at the respective accommodation positions without causing the frontmost lens group and the rear lens group to come into contact with each other regardless of the adjustment of the supporting position of the lens supporting frame.
The support frame movement mechanism can include a biasing device; and the support frame movement mechanism can bring the lens supporting frame and the second moving frame into contact with each other, with a biasing force of the biasing device, when the first moving frame and the second moving frame are positioned at the respective accommodation positions.
The support frame movement mechanism can include a first cam follower formed on the first moving frame; a second cam follower formed on the second moving frame; and a cam ring which is driven to rotate about the optical axis, the cam ring including a cam groove in which the first cam follower and the second cam follower are engaged. The cam groove can include a frontmost lens group moving section for moving the first moving frame to the ready-to-photograph position; a rear lens group moving section for moving the second lens frame to the ready-to-photograph position; a frontmost lens group accommodation section for allowing the frontmost lens group to move to the accommodation position which is located behind a position of the frontmost lens group in the optical axis direction when the first cam follower is positioned in the frontmost lens group moving section; and a rear lens group accommodation section for allowing the rear lens group to move to the accommodation position which is located behind a position of the rear lens group in the optical axis direction when the second cam follower is positioned in the rear lens group moving section. The frontmost lens group accommodation section defines a clearance between the frontmost lens group accommodation section and the first cam follower so that the first cam follower is movable in the optical axis direction in the frontmost lens group accommodation section, whereby the frontmost lens group and the rear lens group are not in contact with each other in a state where the lens supporting frame and the second moving frame are in contact with each other when the first moving frame and the second moving frame are located at the respective accommodation positions. The clearance includes at least a predetermined width corresponding to a maximum variation amount by the adjustment of the supporting position of the lens supporting frame.
The support frame movement mechanism can include a first cam follower formed on the first moving frame; a second cam follower formed on the second moving frame; and a cam ring which is driven to rotate about the optical axis, the cam ring including a cam groove in which the first cam follower and the second cam follower are engaged. A width of the cam groove in the optical axis direction at a position corresponding to the accommodation position, when the first moving frame is positioned at the accommodation position, is formed so that a clearance between the cam groove and the first cam follower is greater than an adjustment range of a position of the lens supporting frame relative to the first moving frame in the optical axis direction.
The biasing device can include at least one helical compression spring.
In another embodiment, a lens barrel can include at least one lens group which moves in an optical axis direction; a ring member which is provided around the lens group, the ring member having a photographing aperture at a front end of the ring member; and at least one barrier blade positioned at the front end of the ring member, the barrier blade being driven to open and close the photographing aperture. A frontmost surface of the lens group can be formed as a convex surface. The barrier blade can include a concave surface which is formed on a rear surface thereof so that a shape of the concave surface corresponds to a shape of a corresponding portion of the frontmost surface. The barrier blade can be driven to open and close the photographing aperture in a plane perpendicular to the optical axis at a position where collision between the barrier blade and the convex front surface of the lens group is avoided due to the presence of the concave surface.
It is desirable for the lens group to include a front lens group and a rear lens group, the extendable lens barrel further including a front lens support member which supports the front lens group and is guided in the optical axis direction without rotating about the optical axis; a rear lens support member which supports the rear lens group and is guided in the optical axis direction without rotating about the optical axis; and a support frame movement mechanism for moving the front lens support member and the rear lens support member between respective ready-to-photograph positions and respective accommodation positions located behind the respective ready-to-photograph positions in the optical axis direction, respectively. The support frame movement mechanism can bring the front lens support member and the rear lens support member into contact with each other at the respective accommodation positions without causing the front lens group and the second lens group to come into contact with each other.
The support frame movement mechanism can include a biasing device, and the support frame movement mechanism can bring the front lens support member and the rear lens support member into contact with each other, with a biasing force of the biasing device, at the respective accommodation positions.
It is desirable for the front lens group to include a frontmost lens group of the lens group. The front lens support member includes a lens supporting frame to which the frontmost lens group is supported, and a first moving frame to which the lens supporting frame is supported via male and female screw-threaded portions meshing with each other, one and the other of the male and female screw-threaded portions being formed on the lens supporting frame and the first moving frame, respectively. A supporting position of the lens supporting frame, relative to the first moving frame in the optical axis direction, can be adjusted via the male and female screw-threaded portions during assembly. The support frame movement mechanism can bring the lens supporting frame and the rear lens support member into contact with each other when positioning the front lens support member and the rear lens support member at the respective accommodation positions without causing the frontmost lens group and the rear lens group to come into contact with each other regardless of the adjustment of the supporting position of the lens supporting frame.
The lens group can constitute a lens element of a zoom lens optical system for varying a focal length.
The barrier blade can include a pair of barrier blades; and the concave surface can include a pair of semi-circular concave faces which are formed on the pair of barrier blades, respectively, the pair of semicircular concave faces together forming a circular concave face, the circular concave face corresponding to the shape of a central portion of the convex frontmost surface in a state where the pair of barrier blades are closed.
In another embodiment, a lens barrel is provided, including front and rear lens groups guided in a direction of an optical axis without rotating about the optical axis; a first support frame which supports the front lens group, the first support frame including a first cam follower; a second support frame which supports the rear lens group, the second support frame including a second cam follower; and a cam ring which is driven to rotate about the optical axis, the cam ring including a first groove portion and a second groove portion in which the first cam follower and the second cam follower are engaged, respectively. The first groove portion includes a first operating section for moving the front lens group to a position wherein a photographing operation is performed; and a first accommodation section for moving the front lens group to a first accommodation position which is located behind a position of the front lens group in the optical axis direction when the first cam follower is positioned in the first operating section. The second groove portion includes a second operating section for moving the rear lens group to perform the zooming operation; and a second accommodation section for photographing the rear lens group to a second accommodation position which is located behind a position of the rear lens group in the optical axis direction when the second cam follower is positioned in the second photographing section. At least one of the first accommodation section and the second accommodation section is formed to allow corresponding at least one of the first cam follower and the second cam follower to move in the optical axis direction in corresponding the at least one of the first accommodation section and the second accommodation section.
The first accommodation section and the second accommodation section can be formed so that the front lens group and the rear lens group are released from constraints of the first accommodation section and the second accommodation section at the first accommodation position and the second accommodation position, respectively.
The cam groove can be formed as a continuous groove including the first groove portion and the second groove portion.
It is desirable for the first groove portion, the second groove portion, the first accommodation section and the second accommodation section to be arranged in that order from one end of the cam groove, so that the first cam follower passes through the second groove portion when moving between the first accommodation section and the first groove portion.
The second operating section of the second cam groove can be formed adjacent to the first operating section of the first cam groove portion, and the first accommodation section of the first cam groove portion can be formed adjacent to the second operating section, and the second accommodation section of the second cam groove can be formed adjacent to the first accommodation section.
In another embodiment, a lens barrel is provided, including a plurality of lens groups guided in an optical axis direction without rotating about the optical axis; a plurality of support frames which support the plurality of lens groups, respectively; a plurality of cam followers formed on the plurality of support frames, respectively; and a cam ring which is driven to rotate about the optical axis, the cam ring including a plurality of cam grooves in which the plurality of cam followers are engaged, respectively. Each of the plurality of cam grooves includes an operating section for moving corresponding one of the plurality of lens groups to perform a photographing operation; and an accommodation section for moving the corresponding one lens group to an accommodation position which is located behind a position of the corresponding one lens group in the optical axis direction when corresponding one of the plurality of cam followers is engaged in the operating section. The accommodation section is formed to allow the corresponding one cam follower to move in the optical axis direction in the accommodation section.
The present disclosure relates to subject matter contained in Japanese Patent Applications Nos. 2001-83262, 2001-83263, 2001-83683, 2001-83684 and 2001-83691 (all filed on Mar. 22, 2001) which are expressly incorporated herein by reference in their entireties.